title: Mechanisms of metformin inhibiting lipolytic response to isoproterenol in primary rat adipocytes.
abstract: The mobilization of free fatty acids (FFA) from adipose tissue to the bloodstream primarily depends on triacylglycerol lipolysis in adipocytes. Catecholamines are major hormones that govern lipolysis through elevating cellular cAMP production and activating protein kinase, cAMP dependent, catalytic, alpha (PKA) and mitogen-activated protein kinase 1/2 (MAPK1/3). Obesity and type 2 diabetes are associated with elevated levels of systemic FFA, which restricts glucose utilization and induces insulin resistance. The biguanide metformin exerts its antihyperglycemic effect by enhancing insulin sensitivity, which is associated with decreased levels of circulating FFA. In this study, we examined the characteristics and basis of the inhibitory effect of metformin on adrenergic-stimulated lipolysis in primary rat adipocytes. We measured the release of FFA and glycerol as an index of lipolysis and examined the major signalings of the lipolytic cascade in primary rat adipocytes. Metformin at 250-500 microM efficiently attenuated FFA and glycerol release from the adipocytes stimulated with 1 microM isoproterenol. To elucidate the basis for this antilipolytic action, we showed that metformin decreased cellular cAMP production, reduced the activities of PKA and MAPK1/3, and attenuated the phosphorylation of perilipin during isoproterenol-stimulated lipolysis. Further, metformin suppressed isoproterenol-promoted lipase activity but did not affect the translocation of lipase, hormone-sensitive from the cytosol to lipid droplets in adipocytes. This study provides evidence that metformin acts on adipocytes to suppress the lipolysis response to catecholamine. This antilipolytic effect could be a cellular basis for metformin decreasing plasma FFA levels and improving insulin sensitivity.
authors.affiliation: Department of Physiology and Pathophysiology, Peking University Health Science Center, 38 Xueyuan Road, Beijing 100191, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Zhang
authors.forename: Jinhan
authors.initials: J
authors.lastname: He
authors.forename: Chong
authors.initials: C
authors.lastname: Xu
authors.forename: Luxia
authors.initials: L
authors.lastname: Zu
authors.forename: Hongfeng
authors.initials: H
authors.lastname: Jiang
authors.forename: Shenshen
authors.initials: S
authors.lastname: Pu
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Guo
authors.forename: Guoheng
authors.initials: G
authors.lastname: Xu
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology*; D008049:Lipase / Q000378:metabolism; D008066:Lipolysis / Q000187:drug effects*; D008687:Metformin / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D000070778:Perilipin-1; D010750:Phosphoproteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000318:Adrenergic beta-Agonists; D002352:Carrier Proteins; D005230:Fatty Acids, Nonesterified; D007004:Hypoglycemic Agents; D000070778:Perilipin-1; D010750:Phosphoproteins; D008687:Metformin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D008049:Lipase; D007545:Isoproterenol; D005990:Glycerol